Geochemistry of Palaeozoic marine petroleum from the Tarim Basin, NW China: Part 1. Oil family classification

The oils from the Kuqa Depression are easily distinguished from the other two families due to their terrigenous origin. The major characteristics of the Kuqa oils are high Pr/Ph ratio, very low DBT/P ratio, heavy bulk isotopic composition, low PAH alkylation degree, high proportion of C20 and C21 tricyclic terpanes and C24 tetracylic terpane, and abundance of triaromatic dinosteranes and 4-methyl-24-ethyltriaromatic cholestanes. These characteristics are consistent with terrestrial organic source rocks deposited under sub-oxic conditions.